The general objectives of this project are to establish the pathways and study the characteristics of the enzymes involved in the biosynthesis of the diterpenoid gibberellin phytohormones. The relationship of these reactions to other aspects of isoprenoid metabolism in the same tissues will be investigated along with factors which regulate and integrate all of these reactions. Present emphasis is on studies of the microsomal mixed function oxidases involved in kaurene and kaurenoic acid metabolism and associated electron transfer reactions in cell-free extracts of the fungus Fusarium moniliforme. The purification and mechanism of an ATP--stimulated pyridine nucleotide transhydrogenase in the microsomes of immature seed of Echinocystis macrocarpa are under investigation. A number of aspects of diterpene biosynthesis in cell-free extracts of castor bean (Ricinus communis seedlings will be investigated including the purification and comparative characteristics of the prenyl transferase(s) involved in geranyl-geranyl pyrophosphate synthesis, the structure of the diterpenoid phytoalexin casbene, and the nature of the fungal factors inducing casbene synthesis. Affinity columns based on plant growth retardants for the purification of kaurene synthetase and related cyclization enzymes will be developed and tested.